async function async1() {
    console.log('async1 start')
    await async2()
    console.log('async1 end') // 微
}
async function async2() {
    console.log('async2 start')
    await async3()
    console.log('async2 end') // 微
}
async function async3() {
    console.log('async3 start')
    await async4()
    console.log('async3 end') // 微1
}
async function async4() {
    console.log('async4')
}
console.log('script start')
setTimeout(function () {
    console.log('settimeout')
})
async1()
new Promise(function (resolve) {
    console.log('promise1')
    resolve()
}).then(function () {
    console.log('promise2') // 微
})
console.log('script end')

// script start
// async1 start
// async2 start
// async3 start
// async4
// promise1

// promise2
// script end
// settimeout
